Electrically disbonding materials

ABSTRACT

An electrochemically disbondable composition is provided having a matrix functionality and an electrolyte functionality. The matrix functionality provides an adhesive bond to a substrate, and the electrolyte functionality provides sufficient ionic conductivity to the composition to support a faradaic reaction at an interface with an electrically conductive surface in contact with the composition, whereby the adhesive bond is weakened at the interface. The composition may be a phase-separated composition having first regions of substantially matrix functionality and second regions of substantially electrolyte functionality. Adhesive and coating compositions and methods of disbonding also are described.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This invention was made with United States government support underContract No. F08635-97-C-0036 awarded by the U.S. Department of the AirForce. The United States government has certain rights to thisinvention.

BACKGROUND OF THE INVENTION

The invention relates to materials for use as coatings and adhesivesthat may be disbonded from a surface to which they are applied withoutharm to that surface. The invention further relates to methods ofdisbonding adhesives and coatings from substrate surfaces.

Adhesive bonds and polymeric coatings are commonly used in the assemblyand finishing of manufactured goods. Adhesive bonds are used in place ofmechanical fasteners, such as screws, bolts and rivets, to provide bondswith reduced machining costs and greater adaptability in themanufacturing process. Adhesive bonds distribute stresses evenly, reducethe possibility of fatigue, and seal the joints from corrosive species.Similarly, polymer-based coatings are commonly applied to the exteriorsurface of manufactured products. These coatings provide protectivelayers that seal the surface from corrosive reactants, as well asprovide a painted surface that can be more aesthetically pleasing.

Among the best adhesives and coatings in terms of strength anddurability are those based on thermosetting polymers. Typically appliedas a liquid mixture of low molecular weight monomers, these adhesiveswet and penetrate pores on the substrate surface. On cure, insoluble andinfusible crosslinked polymers are formed that are mechanicallyinterlocked and often covalently bound to the substrate to which theyare applied. Common amine-cured epoxies are a typical example ofadhesives and coatings that employ thermosetting mixtures.

Although adhesive bonds offer many advantages over mechanical fasteners,adhesive bonds are essentially permanent. There are no methods availablefor ready disassembly of adhesively bonded objects. The separationstrategies that do exist typically involve time-consuming chemicalprocedures requiring high temperatures and aggressive chemicals.Examples of such techniques are described in U.S. Pat. No. 4,171,240 byWong and U.S. Pat. No. 4,729,797 by Linde et al. These techniques,although generally effective, are quite harsh and can damage the objectsbeing separated, making them unsuitable for many applications.

Similarly, conventional coating materials, such as polyurethanes,epoxies, phenolics, melamines, and the like, are essentially permanent.Such coatings are often removed with an aggressive chemical agent thatis applied to the coating surface to degrade the coating material.Mechanical abrasion, such as sand blasting or wire brushing, is alsoemployed. Although these techniques are effective in removing thepolymer coating, they are time and labor intensive, as well as beingquite harsh and likely to cause damage to the underlying surface.

To provide materials that are more easily removed from a substrate, theprior art describes adhesives formed from reactive monomers containinglinkages susceptible to chemical degradation. Such materials aredescribed in U.S. Pat. Nos. 5,512,613 and 5,560,934 to Afzali-Ardakaniet al. and in U.S. Pat. No. 4,882,399 to Tesoro et al. Additionally, S.Yang et al in “Reworkable Epoxies: Thermosets with Thermally CleavableGroups for Controlled Network Breakdown”, Chem. Mater. 10:1475 (1998)and Ogino et al. in “Synthesis and Characterization of ThermallyDegradable Polymer Networks”, Chem. Mater. 10(12):3833 (1998) describecurable resins containing thermally labile linkages. Other polymerscontaining thermally labile or thermally reversible crosslinks aredescribed in U.S. Pat. No. 3,909,497 to Hendry et al. and U.S. Pat. No.5,760,337 to Iyer et al. An alternative approach to bond cleavage isdescribed in U.S. Pat. No. 5,100,494 to Schmidt which disclosesembedding a nichrome heating element within a thermoplastic so that theadhesive softens or melts upon resistive heating. Although thesespecially prepared materials are more readily cleaved from thesubstrate, they still require conditions that are harsh to delicatesubstrates or adjacent adhesive bonds.

Thus, there remains a need in the art for a material capable of beingdisbonded selectively and precisely under mild conditions. Such amaterial would provide adhesive bonds and coatings that could beemployed in a variety of applications where facile removal of thematerial from the surface is desired.

SUMMARY OF THE INVENTION

The present invention provides a composition capable of strong, yettemporary, substrate bonding or coating that is removable without damageto the underlying substrate. It may be used in both temporary andpermanent bonding and coating applications.

An electrochemically disbondable composition of the invention includes amatrix functionality and an electrolyte functionality. The matrixfunctionality provides an adhesive bond to a substrate, and theelectrolyte functionality provides sufficient ionic conductivity to thecomposition to support a faradaic reaction at an interface with anelectrically conductive surface in contact with the composition. Theadhesive bond is weakened at the interface on application of anelectrical potential across the interface. In preferred embodiments, thedisbondable composition is a phase separated material having firstregions of substantially matrix functionality and second regions ofsubstantially electrolyte functionality.

The “matrix functionality” of a material is the ability of a material ora mixture of materials to join by mechanical or chemical bonding to asubstrate and to adhere to the substrate by virtue of this bond. Matrixfunctionality also provides mechanical strength to the material, suchthat the material is capable of transferring load between substrates or,as a coating, is self-supporting.

The “electrolyte functionality” of a material is the ability of thematerial to conduct ions, either anions, cations or both. The ions areprovided by a salt added to the material or are chemically incorporatedinto the material as an ionomer, that is, a polymer containing ionizedgroups. The electrolyte functionality is understood to derive from theability of the composition to solvate ions of at least one polarity.

The term “faradaic reaction” means an electrochemical reaction in whicha material is oxidized or reduced.

The term “adhesive” refers to polymer-based materials which are capableof holding materials together by surface attachment. An adhesivetypically forms a bond to a substrate by mechanical interlocking andoften covalent bonding to the substrate. The adhesive is chemicallydistinct from the bonded substrate and the bonded materials may bedissimilar from one another.

In one embodiment of the invention, the matrix functionality is providedby a polymer selected from the group consisting of epoxies, phenolics,acrylics, melamines, maleimides, and polyurethanes.

In another embodiment of the invention, the polymer has a variablecrosslink density to form regions of low crosslink density having arelatively high ionic conductivity and regions of high crosslink densityhaving a relatively high mechanical strength.

In another embodiment of the invention, the polymer includescoordination sites that are capable of solvating ions and that supportthe electrolyte functionality of the composition.

In other embodiments, the electrolyte functionality is provided by anelectrolyte additive selected from the group consisting of ionicallyconductive monomers, oligomers and polymers, and ionomers and may belocalized in regions within said polymer to form a secondary phase ofhigh ionic conductivity and mobility.

In one preferred embodiment, the disbondable composition is an adhesive,and may have a lap shear strength in the range of 2000-4000 psi. Inanother preferred embodiment, the composition is a coating, and may beresistant to delamination from a substrate to which it is applied.

In another aspect of the invention, an electrochemically disbondablecomposition is provided having an uncured polymeric material having anelectrolyte located therein. The uncured polymeric material, when cured,provides in combination with the electrolyte, sufficient solubility andmobility to the electrolyte to support a faradaic reaction at a surfacein electrical contact with an electrode.

Another aspect of the invention includes a corrosion resistant coatingin which a substrate subject to corrosion has as a coating a compositionhaving a matrix functionality and an electrolyte functionality, saidmatrix functionality providing an adhesive bond to said substrate, andsaid electrolyte functionality providing sufficient ionic conductivityto said composition to support a faradaic reaction at an interface withsaid substrate. Corrosion of the substrate does not propagate at theinterface.

In yet another aspect of the invention, a bonded structure includes twoelectrically conductive surfaces, and a bond between the two surfacescomposed of the electrochemically disbondable composition of theinvention. The conductive surface may be an article or articles to besecured by the bond or they may be a conductive element selected fromthe group consisting of sheets, foils, grids and meshes. The conductiveelement further may be bonded to an article using a conventionaladhesive or the disbondable composition of the invention.

In one embodiment of the invention, the electrically conductive surfaceis an electrically conductive coating applied to a substrate, which maybe non-electrically conducting.

In another embodiment of the invention, the bonded structure includesfirst and second electrically conductive surfaces; and an electricallyconductive element disposed therebetween. The electrochemicallydisbondable composition of the invention is used to bond theelectrically conductive element to the first and second conductivesurfaces.

A laminate structure is also provided which is particularly advantageousin the joining of irregular or non-conductive surfaces. The laminateincludes first and second electrically conductive elements selected fromthe group consisting of foils, sheets, meshes and grids, and thedisbondable composition of the invention disposed therebetween andbonded to the first and second elements.

In another aspect of the invention, a method is provided for disbondinga composition from an electrically conductive surface to which it isbonded. The method includes providing a first electrically conductivesurface treated with the electrochemically disbondable composition ofthe invention, contacting a second electrically conductive surface tothe composition, and passing an electric current through the disbondablecomposition to cause a faradaic reaction at the surface, whereby thebond to the surface is weakened.

The bond between the disbondable composition and a substrate may beweakened in a short time by the flow of electrical current across thebondline between the substrate and the composition. Typically, the bondis weakened sufficiently that the substrate is separated easily by handfrom the disbondable composition. At least one of the substratesseparates cleanly and is substantially free from any residual bondingcomposition. Because the disbonding procedure uses electricity insteadof heat or chemical reagents, inadvertent disbonding during normal useis unlikely.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described with reference to the figures which arepresented for the purpose of illustration only and which are notlimiting of the invention, and in which:

FIG. 1 is a cross-sectional illustration of a bonded joint using thecomposition of the invention and of the disbonding operation of theinvention;

FIG. 2 is a cross-sectional illustration of an embodiment of theinvention incorporating a conductive foil into a bonded structure;

FIG. 3 is a cross-sectional illustration of an embodiment of theinvention incorporating a conductive coating into a bonded structure;

FIG. 4A-C are illustrations of bonded articles of the inventionincorporating electrically conductive sheets or coatings in the bondedstructure;

FIG. 5 is an illustration of a bonded joint and electrical circuitry forsimultaneous disbonding at more than one interface in a bonded joint;and

FIG. 6A is a perspective drawing and 6B is a cross-sectionalillustration of a laminate bonded structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electrochemically disbondable composition of the invention possessesmatrix functionality and electrolyte functionality, where theelectrolyte functionality provides sufficient ionic conductivity tosupport a faradaic reaction at an electrically conductive substrate incontact with the composition. The matrix functionality of thedisbondable composition provides the adhesive or coating propertiesneeded for its intended use, while the electrolyte provides the ionicconductivity and ion mobility needed to maintain the faradaic reaction.

The electrically conductive substrate may be a surface of the articlebeing bonded or coated. Alternatively, the electrically conductivesubstrate may be one added to the coating or bond to provide anelectrochemically cleavable surface.

The adhesive property of the composition is disrupted by the applicationof an electrical potential across the bondline between the compositionand substrate. While not bound to any particular mode of operation, thefaradaic reactions which take place at the composition substrateinterface are presumed to disrupt the interaction between thedisbondable material and the substrate, thereby weakening the bondtherebetween. Disruption at the adhesive interface may be the result ofa number of processes taking place at the interface, such as chemicaldegradation of the disbondable material, gas evolution at the substrateinterface and/or material embrittlement, possibly by changes incrosslink density of the disbondable composition.

Matrix functionality may be provided by one of the general classes ofpolymers and polymer resins used in bonding or coating surfaces. Thematerials may be prepared from commercially available polymer resins,often without modification.

The polymer may be a thermoset polymer, which provides high strength andsolvent resistance to the bond or coating, but which is difficult toremove from the surface. A thermoset polymer is one in which a linear orcrosslinked network extends throughout the final composition to providea polymer that is stable to heat and that does not flow or melt. Thepolymer is typically formed by in situ reaction or curing of lowermolecular weight species, e.g., epoxies, or by the chemicaltransformation of soluble precursor polymers, e.g., formation ofpolyimide from polyamic acid. Exemplary thermosetting polymers includehighly condensed polyimides, polyurethanes, epoxies, phenolic resins,urea or melamine formaldehyde condensates, acrylic resins and alkydresins. A preferred polymer resin for use as an adhesive or a coating isepoxy.

The polymer may also be a thermoplastic which is thermally tractable andcan be made to soften or flow with the application of heat. Thesepolymers are linear or lightly branched and are typically soluble insome solvent. Exemplary thermoplastic polymers include acrylics, styrenebutadiene block copolymers and the like.

The above polymers are well suited to provide the matrix functionalityof the composition; however, in order to support a faradaic reaction atan electrically conductive substrate, the disbonding composition alsomust possess sufficient ion conductivity to permit ion transport withinthe composition. Modification of the polymer to promote or support ionicconductivity or to promote ion solubility therefore is contemplated.

In one embodiment of the invention, the polymer includesion-coordinating moieties that are capable of solvating ions, and inparticular cations, of the electrolyte. Exemplary ion-coordinatingmoieties include alkoxy groups, such as methoxy or ethoxy, andoligoethers, such as polyethylene oxide and the like, disulfidemoieties, thioalkyl groups, alkyl or alkenyl nitrile groups andpolyvinylidene fluoride groups. By way of example only, an epoxy resinmay be cured using a diamine having a high alkoxy content to provideadditional oxygen sites for cation coordination. Example 2 describes theuse of the diamine, 4,7,10-trioxy-1,13-tridecanediamine, for thispurpose.

Another manner in which the polymer supports or promotes the dissolutionand diffusional movement of the ions found in the electrolyte is to havea glass transition temperature T_(g) that is below the disbondingtemperature. This can be achieved by increasing the disbondingtemperature, or adding a plasticizer to the polymer composition. Theterm “plasticizer” means an electrochemically stable additive whichtends to reduce the crystallinity or order of the composition. Exemplaryplasticizers include alkyl carbonates, low molecular weight alkoxides,cyclic esters, alcohols, nitriles, amides and ureas. Many otherplasticizers well-known to skilled artisans may also be employedadvantageously to lower T_(g). It can be additionally advantageous ifthe plasticizing molecules are capable of solvating ions, as are theabove-mentioned exemplary plasticizers. By solvating ions, theplasticizer additive increases the concentration of salts that may beadded to the composition to provide ionic conductivity (see below).

Heterogeneous curing can also be used to affect a low T_(g). Aheterogeneously cured thermosetting resin is one in which the crosslinkdensity or degree of polymer condensation varies throughout thecomposite resulting in regions of high and low glass transitiontemperatures. This may be achieved by locally varying the amount ofcrosslinking or curing agent in the polymer.

In one embodiment of the invention, a heterogeneously cured polymer isobtained by adding a component to the polymer resin which serves as areservoir for excess curing agent or crosslinking agent. Exemplaryreservoirs include porous ceramics such as zeolites, clays or polymergels. By way of example only, a zeolite may be infused with an excess ofamine curing agent and mixed into an epoxy polymer resin. The presenceof the excess amine during a thermally activated cure results in theformation of a heterogeneous material having local regions of high aminecontent and low crosslink density near the zeolite particles embedded ina matrix of stoichiometric, high crosslink density material. Ideally,the regions of low crosslink density connect to form continuous pathwayswith lower glass transition and higher ionic conductivity.

In some embodiments of the invention, the electrochemically disbondablecomposition includes a separate electrolyte phase to provide theelectrolyte functionality of the disbondable composition. An electrolytemay be used in combination with any of the above-mentioned polymers. Theelectrolyte may be an ionically solvating molecule, including aplasticizer, or an oligomer or polymer also capable of solvating ions.Typically, ion solvation is obtained with polar molecules or moleculesthat are easily polarized. The electrolyte may also constitute a portionor region of a polymer which is added to the composition. For example,the disbondable composition may include a block or graft copolymerhaving regions of high ionic conductivity and regions having some otherdesirable property, such as compatibility with the polymer resin. Thepolymer resin-miscible domains promote dispersion of the block copolymerthroughout the entire resin, with the polar, ionically conductiveregions associated into domains or micelles. Without the polymerresin-miscible domains, certain combinations of polymer and electrolytemay not be sufficiently compatible to form a cohesive composition andmechanical and/or adhesive strength would be compromised.

The electrolyte functionality of the disbondable composition providesionic conductivity sufficient to maintain a faradaic reaction at aninterface with an electrically conductive surface. Sufficientconductivity may be readily established by preparing a composition andapplying a voltage across a bondline with an electrically conductivesubstrate. If current flow is observed, a faradaic reaction at thebondline may be assumed. Sufficient ionic conductivity also may beempirically observed by applying a voltage across the bondline andnoting whether the bond is weakened. Compositions with ionicconductivities in the range of 10⁻¹¹ to 10⁻⁵ S/cm at room temperatureare considered within the scope of the invention. Materials havinghigher ionic conductivities require shorter disbanding times.Compositions with ionic conductivities in the range of 10⁻⁹ to 10⁻⁷ S/cmat room temperature are preferred.

The electrolyte is desirably ionically conductive and capable ofsupporting ion diffusion of a salt solvated therein. In mostembodiments, complex ion salts are added to the composition to provideionic conductivity. Suitable salts include alkali metal, alkaline earthand ammonium salts. Preferred salts include polyatomic, highdissociation constant anions, such as hexafluorophosphate,tetrafluoroborate, hexafluoroantimonate and perchlorate.

In another embodiment, the electrolyte functionality is provided by anionomer. The ionomer is a polymer or oligomer with ionized groups thatprovide ions capable of being solvated in the composition.

The electrolyte is included in the disbondable composition in an amountsufficient to provide the requisite ionic conductivity to support thefaradaic reaction of the disbonding process. The actual amount ofelectrolyte used in a particular composition is dependent on the ionicconductivity of the polymer and the ability of the electrolyte to form acontinuous conductive pathway within the composition. While a continuouspathway is not absolutely required, it promotes the efficiency of theprocess. Where ions are required to tunnel through regions of higherresistance, higher voltages and longer times are required fordisbonding.

In preferred embodiments, approximately equal volumes of the matrixpolymer and the electrolyte are used, although a wider range ofcompositions is contemplated as within the scope of the invention. Thoseskilled in the art are aware that a wide range of compositions may beused to obtain a substantially continuously conductive electrolyte tophase depending upon the materials used and how the composition phaseseparates. In some instances, a seemingly high level of electrolyte,e.g., 50 vol %, may be added without overly compromising the adhesive ormechanical properties of the disbondable composition. The composition ispresumed to maintain its strength due to the ionic strengtheningtypically observed in polymeric systems containing salts or ionomers.Ionic domains may form, acting as pseudo-crosslinks in the ionicallyconductive regions or as crosslinks between the conductive region andthe matrix polymer.

In preferred embodiments, the disbondable composition is aphase-separated composition having regions enriched in electrolytehaving high ionic conductivity and regions enriched in matrix polymerhaving high mechanical or bonding strength. A phase-separatingcomposition may comprise an initially miscible mixture of polymer resinand electrolyte. The electrolyte may segregate from the growing resinnetwork during cure. Phase separation may be encouraged by increasingthe molecular weight of the polymer resin, oligomeric (or polymeric)electrolyte additive, or both.

In preferred embodiments, phase separation results in regions havinghigh ionic conductivity forming a continuous pathway within thecomposition. Without a continuous pathway, ions are required to traversethe high strength, low conductivity regions of the material duringelectrochemical disbonding. Bicontinuous or interpenetrating networksadvantageously provide a continuous ionically conductive pathway withoutcompromise to the mechanical strength of the adhesive polymer resin.Phase-separated compositions having the desired microstructure may beobtained by varying the relative proportions of the various componentsof the disbondable composition. For example, a composition comprisingapproximately equal parts by volume of polymer and electrolyte may cureto provide a continuous ionically conductive pathway.

A preferred electrolyte additive for formation of a phase-separatedmicrostructure is a graft copolymer having a backbone with a lowaffinity for the polymer resin and pendant polymer blocks of high ionicconductivity. The low affinity backbone serves as a nucleation point forphase separation by generating small non-solubilized domains within thepre-cured resin, while the high ionically conductive pendant polymerblocks interact with the matrix polymer resin. During cure, theionically conductive polymer phase separates from the curing resin andgrows around the low solubility domains which results in a welldispersed and continuous network. An exemplary graft copolymer includesa siloxane backbone grafted with amine-terminated poly(ethylene glycol)pendant blocks. A graft copolymer may be a comb polymer. The combpolymer is a graft copolymer in which blocks or pendant oligomericchains of a dissimilar polymer are more or less regularly repeated alongthe polymer backbone.

In a further embodiment of the invention, the cohesive strength of thedisbonding composition may be enhanced through the use of ionicallymodified oligomers (as the electrolyte component). For example,amine-functionalized oligomers (such as the amine-terminatedpoly(siloxane)-graft-poly(ethylene glycol) described above) may beconverted to the corresponding ammonium salt by ion exchange of theamino group with an ammonium cation. The resulting highly viscouselectrolyte is readily miscible with polymer resins, and in particularwith amine-curable epoxy resins. A mixture of approximately equalvolumes of the ion-exchanged electrolyte and epoxy resin can be cured toform a high cohesive strength adhesive material possessing sufficientionic conductivity to support electrochemical disbonding.

While the invention has been described primarily with reference toepoxides, other polymer resins may be used in accordance with theinvention.

For example, bismaleimides may be directly substituted for epoxies inthe electrochemical disbondable formulations. Selection of theappropriate bismaleimide is made to ensure adequate phase separation ofthe polymer matrix phase from the ionically conducting phase. The highlypolar, ion coordinating ability of the cyclic imide group may result incompatibilizing ionic interactions occurring between the two phases. Toovercome this, the bismaleimide can be modified to decrease its polarityin order to increase cure-induced phase separation. These adjustmentsare made empirically to achieve phase separation, while controlling thephase dimensions and degree of mechanical connectedness between thephases.

Admixtures of a comb polymer, such as those described above, withmonomers of thiols and trienes according to eq. 1 would also yield ahomogeneous mixture. Free radical polymerization by thermaldecomposition of azobis(isobutylnitrile) (AIBN) would result in networkpolymer formation and phase separation of the comb polymer. Control ofphase morphology, dimension and interphase interaction are also mediatedby inclusion of ammonium salt modified alkyl thiols.

In another embodiment of the invention, phenolic or melamine resins areused for the disbondable material of the invention. Self-condensingresins such as phenolics or melamine (urea)/formaldehyde may be modifiedwith ionically conductive oligomers or polymers and then cured to formphase separated materials provided that the ionically conductiveadditive contains no functionalities that will condense withformaldehyde. Phase separation is controlled by adjusting the moietiespresent in the matrix resin and ionically conductive additive to favorlate-stage phase separation and possibly by pre-seeded nucleation usingcompatible/incompatible copolymer blocks, as is discussed hereinabove.Ionic modification, most likely using sulfonate or ammonium groups toboth the matrix resin and ionically conductive additive, could be usedto control phase morphology, dimension and interphase reactions.

It is understood that additives may be included in a disbondingcomposition so long as they do not compromise the bonding strength orionic conductivity of the composition. Exemplary additives includepigments for color, corrosion inhibitors, leveling agents, glosspromoters and fillers. Other polymer resin additives, known to those ofskill in the art, such as rubber tougheners, e.g.,poly(acrylonitrile-co-butadiene), may be added to increase electrolytesolubility or enhance other desirable properties of the resin. Thedisbondable composition further may include particles of anon-conducting material, e.g., crushed glass or plastic beads, toprevent conductive surfaces useful in the disbonding process fromcontacting each other and forming a short circuit. Other additives willbe apparent to those skilled in the art and are within the scope of theinvention.

The solubilizing ability of the uncured composition and the post-curedcomposition may differ. Thus, initially soluble additives may beexcluded from the composition as it cures. In some embodiments,additives may be selected for incorporation into the disbondablecomposition to retain their solubility in the cured polymer. In otherembodiments, differing pre- and post-cured solubilities may be used toadvantage in obtaining phase-separated materials (see below).

The disbondable compositions may be used as adhesives. A bonded jointmay be obtained by disposing a disbondable composition between two ormore surfaces such that the composition forms an adhesive bond to eachsurface and holds each surface in a generally fixed position relative tothe other surfaces while maintaining those positions in response to aforce equal to at least the weight of the lightest bonded element.

A bonded joint may be obtained by applying an adhesive of the inventionto a suitable surface as a solution, a melt or a reactive mixture.Solvents, if used, may be removed by evaporation prior to mating thesubstrates or may be absorbed by the coated substrate. Compositionsapplied as a melt, a solution or a reactive mixture wet the substratesand then solidify in order to achieve a high level of adhesion. Whenapplied as a reactive mixture, the composition undergoes a curingreaction that converts the fluid-like mixture to a solid. The lattermethod of application is typically used for common two-componentadhesives, such as conventional epoxies.

The disbondable material of the invention may also be applied as acoating to a substrate surface. Due to the material's anti-corrosiveproperties (discussed hereinbelow), it is advantageously employed as anundercoating or primer layer. As in the formation of a bonded joint, thedisbondable material may be applied to a suitable surface as a solution,a melt or a reactive mixture. It is within the scope of the skilledartisan to prepare formulations suitable for coating applications.

The strength of an adhesive bond may be determined in various ways.Typically, lap shear strengths are used as a measure of the strength ofan adhesive bond. Shear strength is the force required to separate twooverlapping plates when pulling in a direction parallel to the plane ofthe plates. Following ASTM procedure D-1002, an Instron tester orsuitable alternative instrument is used for this purpose. Bonds formedusing disbondable compositions are capable of high strength, havingshear strengths of greater than 200 psi, preferably on the order of 1000psi, and more preferably 2000 psi and as high as 4000 psi. Disbondablecompositions employing epoxies for matrix functionality generallyprovide shear strengths in the range of 2000-4000 psi using thisconfiguration. This is comparable to the shear strengths of conventionalepoxy resins. Thus, it is possible to form an electrochemicallydisbondable joint without compromise to the mechanical strength of thebonded materials.

As described previously, ionic conductivity is a necessary feature ofthe disbondable composition. The rate of the disbonding faradaicreaction, and hence the time necessary to achieve the desired level ofbond weakening, is determined by the ionic current flowing through thecomposition. This current can be measured in the external circuit usingan ammeter. The magnitude of the current is small, typically less than 1mA/cm² of bonded area when the disbonding voltage is initially applied.The current further decreases with time, often decaying to 0.2 mA/cm² orless after one minute. Although the relationship between current anddisbonding voltage is not strictly linear, the use of higher disbondingvoltages results in higher currents and more rapid disbondment.Likewise, the use of low disbonding voltages results in longerdisbondment times. The practitioner may select a disbonding voltage froma few volts to greater than 100 volts depending on the desireddisbondment time and other considerations such as safety and the need toprevent damage to voltage-sensitive substrates.

The disbondment time at a particular disbonding voltage also depends onthe ionic conductivity of the composition. Higher ionic conductivitiespermit higher currents at a given voltage and correspondingly support anincrease in the rate of the disbonding reaction. However, the disbondingreaction occurs substantially at the interface between the compositionand the substrate and the amount of faradaic charge (the time integralof the faradaic current) required to effect disbondment is very small.Therefore, to achieve disbonding in a practical period of time requiresonly a small current and the level of ionic conductivity which is neededto support this activity is relatively low. This feature is advantageousbecause the formulation of materials with high ionic conductivity leadsto poor adhesive properties and limited mechanical strength.

The magnitude of ionic conductivity suitable for the disbonding processmay be understood by measurement of the ionic conductivity of thedisbondable composition described in Example 3. Ionic conductivity isdetermined using the AC impedance technique in which the compleximpedance of the composition is measured over a wide frequency range(5-10⁵ Hz) and the data is fit to a simple circuit model. This methodhas been previously described; see, MacDonald et al., J. Electroanal.Chem. 200:69-82 (1986). Values for ionic conductivity as a function oftemperature are listed in Table 1.

TABLE 1 Conductivity measurements Temperature (° C.) Conductivity (S/cm)0 1.1 × 10⁻⁸ 20 2.3 × 10⁻⁷ 40 1.6 × 10⁻⁶ 60 7.0 × 10⁻⁶ 80 2.1 × 10⁻⁵

Although the conductivities listed in Table 1 for the composition ofExample 3 are considerably smaller than conductivities of electrolytesused in electrochemical devices (ca. 10⁻³ S/cm), the conductivity issufficient to achieve disbonding in 10 minutes at room temperature withan applied voltage of 50 V.

The foregoing embodiments teach a disbondable composition having matrixand electrolyte functionalities which permit controlled disbonding ofthe composition from an electrically conductive substrate in response toan electrical voltage applied between the substrate and composition.

With reference to FIG. 1, a method includes passing an electricalcurrent through a disbondable composition 10 in contact withelectrically conducting substrates 12, 14 to disrupt the bonding at anadhesive substrate interface 16 and thereby weaken the bondtherebetween. Current is supplied to the composition using an electricalpower source 18. When an electrical voltage is applied between the twosubstrates 12, 14, electrochemical reactions occur at thesubstrate/disbonding composition interfaces. The electrochemicalreactions are understood as oxidative at the positively charged oranodic interface and reductive at the negatively charged or cathodicinterface. The reactions are considered to weaken the adhesive bondbetween the substrates allowing the easy removal of the disbondablecomposition from the substrate. (Note, for the purposes of discussion inall Figures one of the electronically conductive surfaces is designatedas the positive electrode. It is understood that the polarity of thesystem may be reversed.) The electrical power source may supply director alternating current. Direct current may be supplied from a battery oran AC-driven, DC power source.

Most disbonding processes require a voltage of only several volts, forexample, less than 10 volts. However, higher voltages, e.g., on theorder of up to 100 volts, may be useful to overcome the electricalresistance inherent in the system. Very little current, ca. 10⁻³ ampsper square centimeter, is required to complete disbonding. Disbonding isaccomplished rapidly, regardless of the complexity of the surface to bedisbonded. In many cases, a potential is applied for a time period inthe range of about 5 to 60 minutes, and preferably about 10 to 30minutes.

The electrochemically disbondable composition may be selected so thatdisbonding occurs at either the positive or negative interface. Thepositive interface is the interface between the electrochemicallydisbondable composition and the electrically conductive surface that isin electrical contact with the positive electrode. Similarly, thenegative interface is the interface between the electrochemicallydisbondable composition and the electrically conductive surface that isin electrical contact with the negative electrode. Disbonding occurs atthe positive interface for the disbonding compositions described inExamples 1-4 below. By reversing current direction prior to separationof the substrates, the bond may be weakened at both substrateinterfaces.

In an alternative embodiment, alternating current may be used tosimultaneously disbond both substrate/adhesive interfaces. Thisembodiment is particularly useful when removal of the disbondablecomposition from both substrates after disbonding is desired. Typically,the alternating current reverses the anodic and cathodic interfaces on atime scale that is short compared with the total time necessary todisbond the interfaces. The current can be applied with any suitablewaveform, provided sufficient total time at each polarity is allowed fordisbonding to occur. Sinusoidal, rectangular, and triangular waveformsare appropriate. The waveform may be applied from a controlled voltageor a controlled current source.

Alternative formulations may be employed for cathodic disbonding. Suchan embodiment is described in Example 7.

Non-conductive or non-conductively coated substrates my also beelectrochemically disbonded by incorporation of an additional conductingelement to complete the electrical circuit. With reference to FIG. 2, aconducting element 20 is incorporated into the bonding structure inthose instances when one of the substrates 22 is non-conductive orcoated with a non-conductive layer. A voltage is applied between theconducting element 20 and an electrically conductive substrate 24 havinga disbondable composition 10 disposed therebetween. Disbonding occurs ateither conductive element disbonding composition interface 26 or atsubstrate 24 depending on the arrangement of the electrical circuit andthe choice of the composition. Conducting element 20 is bonded on itsopposite face to the non-conducting substrate 22 by adhesive 28, whichmay be either a conventional adhesive or the electrochemicallydisbondable composition of the invention. It is contemplated that theuse of a conducting element in joints and disbonding operations is notlimited to non-conductive substrates and may also be used withconductive substrates.

The electrically conductive element may be any electrically conductingmaterial capable of being embedded between two bonded surfaces.Exemplary elements include, but are not limited to, wire mesh, metalfoil, and a conductive coating, e.g., a silver-filled epoxy. In thoseinstances where the conductive element is a wire mesh or grid, the meshsize should provide adequate surface area contact for the disbondablematerial since bond weakening occurs in those areas in close proximityto the substrate.

FIG. 3 illustrates an embodiment in which the conductive element is aconductive coating 30 coated onto the surface of the non-conductivesubstrate 22.

The method of the present invention can also electrically cleave a bondbetween two electrically non-conductive substrates. Disbonding isaccomplished by using a bonded structure incorporating two electricallyconductive elements. An electrical circuit is completed using theelectrically conductive elements and disbonding occurs at the element.FIG. 4 illustrates several bonded structures of the invention.

FIG. 4A is a bonded structure incorporating two electrically conductivefoils, meshes or grids, 40, 42. The electrochemically disbondablecomposition 10 is disposed therebetween. The elements 40, 42 are bondedto substrates 44, 46, respectively. Substrates 44, 46 may be conductivesubstrates, non-conductive substrates or substrates having anon-conductive coating, although the use of conductive elements isuseful in those instances when both substrates are non-conductive.Conductive elements are bonded to the substrates using eitherconventional adhesives or the disbondable composition of the invention64.

FIG. 4B is a bonded structure incorporating two electrically conductivecoatings 48, 50, which coat substrates 52, 54, and which are inelectrical contact through external wires with a power source tocomplete the electrical circuit. The electrochemically disbondablecomposition 10 is disposed therebetween. Substrates 52, 54 may beconductive substrates, non-conductive substrates or substrates having anon-conductive coating, although the use of conductive elements isuseful in those instances when both substrates are non-conductive.

FIG. 4C is a related bonded structure incorporating an electricallyconductive foil, mesh or grid 42 and an electrically conductive coating48 which coats substrate 52. The electrochemically disbondablecomposition 10 is disposed between the conductive elements 42, 48, whichare in electrical contact through external wires with a power source tocomplete the electrical circuit. Substrates 46, 52 may be conductive ornon-conductive, or substrates having a non-conductive coating. The useof conductive elements is advantageous in those instances when bothsubstrates are non-conductive.

The disbonding operation may also simultaneously disbond more than onesurface, using a setup such as that shown in FIG. 5. The bondedstructure includes a conductive element 42 disposed between twosubstrates 60, 62. Disbondable composition 10 is used in forming thebond. Substrates 60, 62, may be conductive substrates or they mayincorporate conductive elements as described hereinabove to facilitatedisbonding from non-conductive substrates. Both substrates are connectedin parallel to the voltage source at the anode and the conductiveelements serves as the cathode (in embodiments where anodic disbondingtakes place). In operation, the anodic disbonding material/substrateinterfaces are cleaved, leaving a conductive elements coated on bothsides with disbonding material.

A preferred embodiment of the invention includes a metal foil patch orlaminate 69 such as that shown in FIG. 6A. The patch includes a thinlayer of electrochemically disbondable material 70, backed on eitherside by metal foils 72, 74 typically aluminum foil. The patch isflexible and readily conforms to nonplanar surfaces. The patch can becut to size, coated with adhesive and placed between the substrates tobe bonded. Similar to the bonded structures described above, bondedstructures formed using a foil patch may be readily separated at themetal foil by passing an electrical current between the foils.

In all of the above structures and articles, contact may be made withthe conductive substrate or element through conventional means. Clips orother contacting means may be employed. In preferred embodiments, aconductive tab may be spot welded onto the electrically conductivesubstrate or element to improve electrical contact.

In another embodiment of the invention, the composition may beformulated with specific curing agents such that the cured material isremoved from a substrate using solvents that are comparatively benign tothe environment and pose minimal health risk to the practitioner. Thisembodiment is particularly useful following electrical disbonding of acomposition. Residual material of the composition that remains on asubstrate following the disbonding can be readily removed without resortto aggressive chemicals, heat or mechanical means. Thus, for example, anadhesive composition that disbonds at the anodic electrode can beremoved from the cathodic electrode using a solvent such as a lowmolecular weight alcohol, e.g. methanol, ethanol, or the like. Removalof the composition is achieved by solvent swelling that is promoted bythe rapid passage of the low molecular weight alcohol through theiconically conductive phase of the composition. A composition of thisembodiment is described in Example 2.

The disbonding process may also be used to remove material which hasbeen deposited on a substrate as a coating. For example, disbondablematerial is applied to a metal surface as a primer layer, over which aconductive film, such as silver-filled epoxy, and a suitable topcoat isapplied. The coating is removed by attaching a power source to the metalsurface (anode) and the silver-filled epoxy layer (cathode).

Alternatively, a conductive metal foil or plate may be contacted to thedisbondable primer to serve as a cathode. The electrode serves as thecathode, for example, if the composition disbonds at the anodicinterface. Contact is facilitated by placing an ionically conductive gelbetween the coating and the metal plate. Suitable gels comprise apolymer-thickened solution or liquid polymer electrolyte containing thesame salt as is used in the disbonding adhesive, e.g., ammoniumhexafluorophosphate.

In a previous embodiment, the use of compositions that could be swelledby a low molecular weight solvent were described. The same embodimentmay also be usefully employed with coatings on a substrate. Swelling theionically conductive phase of the composition with a low molecularweight solvent increases the ionic conductivity of the conductive phase,which promotes disbonding when an electrical voltage is applied betweenthe substrate and coating.

This approach provides the possibility of selectively removing only aportion of the coating as disbonding only occurs where electrochemistryproceeds. Provided that the conductive path through an individual bondis electrically isolated from that of its neighboring bonds, specificbonds on a common substrate may be weakened without affecting adjacentareas, thereby allowing specific repair or replacement to be made. Veryoften, sporadic damage of coatings on large area surfaces only requireslocal removal and repair. This material allows that to be readilyaccomplished.

Appliques, or pre-formed, contact paper-like coatings are increasinglyused to coat appliances, structures and vehicles. Use of a metallized ormetal foil backed applique attached using the disbonding composition ofthe invention allows ready removal of the applique during refurbishmentoperations.

In another aspect of the invention, a corrosion resistant coating isprovided. The term “corrosion” is used herein to mean an electrochemicalprocess leading to the oxidation of a metallic substrate, usually withthe help of an electrolyte, typically accompanied by the reduction ofatmospheric oxygen or water. A corrosion resistant coating is one thatinhibits or hinders active corrosion processes, i.e., metal oxidation,which would otherwise occur in the absence of the coating. Typically, acorrosion resistant coating such as a paint acts as a barrier layerexcluding water and salts from the metal surface. The coating may alsoinclude corrosion inhibitors which are usually partially soluble inwater.

The disbondable composition of the present invention has been found toprevent underpaint corrosion. Underpaint corrosion is defined as themigration of corrosion under the paint (or similar coating) from a siteat which active corrosion is taking place due to a break in the paintwhich exposes the underlying substrate to a corrosive environment.

According to one embodiment of the invention, the disbondablecomposition is used as an undercoat or primer layer. The undercoat maythen be coated with a second paint layer. The second layer provides theprincipal water and salt barrier.

The inventive composition does not function as a corrosion resistantcoating in the sense that it is a barrier layer. Rather, it functions asa corrosion resistant coating by preventing the spread of corrosion onceit is initiated. It is hypothesized that the ionic osmotic pressure atthe surface is reduced where it is in contact with the electrochemicallydisbondable material due to the presence of mobile ion species in thecoating. Thus, the driving force for corrosive oxidation to propagate onthe surface of the metal (ultimately leading to coating delamination) iseliminated or reduced.

An anti-corrosive coating therefore includes a primer layer comprised ofthe electrochemically disbondable material of the invention and atopcoat functioning as a protective barrier layer. If the barrier layeris compromised, the exposed metallic surface is susceptible to oxidationcorrosion; however, the primer layer prevents its propagation underneaththe coating and thereby prevents delamination of the coating.

The invention is illustrated in the following examples which are notlimiting of the invention, the full scope of which is shown in theclaims which follow the specification.

EXAMPLE 1

This example describes an electrochemically disbondable compositionusing a plasticizer as the ionically conductive component.

A disulfide-linked diepoxide 1 of the following structure wassynthesized according to the procedures outlined by Gilbert et al inMater. Res. Soc. Proc., Polymer/Inorganic Interfaces, 304:49 (1993).

An electrocleavable formulation was made by mixing 100 parts by weightof the above diepoxide with 30 parts of4,7,10-trioxi-1,13-tridecanediamine and 10 parts of amine-terminatedpoly(acrylonitrile-co-butadiene), a rubber toughener (CAS 68683-29-4).To this mixture was added 20 parts each of 1-pentanol and ammoniumhexafluorophosphate. The mixture reacted rapidly at room temperature toyield a cured resin which exhibited very high adhesive bond strengths tocopper. This composition relied upon a combination of a plasticizer andchemical modification of the epoxy, e.g., incorporation ofalkoxy-modified amine curing agent and acrylonitrile copolymer and alsothe disulfide epoxide to gain the requisite ionic conductivity in theproduct composition.

At room temperature, the ionic conductivity of this material is verylow. However, the adhesive bond was electrochemically cleaved in 30minutes by application of a 50-volt potential across the bond-line atelevated temperatures (60° C.).

This formation was also prepared as a solution in nitromethane which canbe spray-coated onto substrates for bonding or coating. This solutionhas a pot-life of several hours, as compared to fifteen minutes for theepoxy mixture without solvent.

EXAMPLE 2

This example describes an electrochemically disbondable compositionusing an ion exchanged graft copolymer,poly[dimethylsiloxane-co-methyl(3-hydroxypropyl)siloxane]-graft-poly(ethyleneglycol) 3-aminopropyl ether, as the ionically conductive component.

In a reaction vessel equipped with a mechanical stirrer,poly[dimethylsiloxane-co-methyl(3-hydroxypropyl)siloxane]-graft-poly(ethyleneglycol) 3-aminopropyl ether (PMS-g-PEO) (75 g), an amine-functionalizedcomb polymer (CAS 133779-15-4) with a M_(n) of ca. 4000 was mixed withammonium hexafluorophosphate (25 g, 0.153 mol) and the mixture wasstirred at 70° C. for 12 hours under vacuum to allow the ion exchangereaction to proceed to completion. The resulting product was a viscous,transparent amber liquid.

A two-part epoxy resin was formulated using the above ion-exchangedPMS-g-PEO. Part A was formulated by blending 100 parts by weightion-exchanged PMS-g-PEO with 75 parts by weight of a low molecularweight (M_(n)=355) diglycidyl ether of bisphenol A (DGEBA) to form aviscous yellow liquid. The blending of the graft copolymer with an epoxyresin promotes dispersion of the electrolyte within the resin, whichpromotes an interpenetrating morphology of the two components of theadhesive composition. Part B was formulated by reacting 25 parts byweight of the DGEBA with 30 parts by weight of4,7,10-trioxa-1,13-tridecanediamine (CAS No. 4246-51-9) to form achain-extended amine curing agent. Chain extension prereacts the epoxyresins to control the curing process and to provide parts of comparableweight in the two-part resin. Crushed glass (3 parts) and blue pigment(copper phthalocyanine) were added to Part B.

The unmixed two-part epoxy resin had a shelf-life of six months or moreat room temperature. It was mixed as a 3:1 ratio of Part A (yellow) toPart B (blue) to give a green-colored paste having a pot life ofapproximately one hour. The paste was applied between aluminum, copperand steel substrates to form bonded structures. The overall chemicalreaction leading to the formation of the disbondable composition is showin Eq. 2.

Lap shear tests were conducted using an Instron tester according to thespecifications of ASTM D-1002, the results of which are reported inTable 2. Lap shear specimens were formed from 1 in.×8 in. metal stripsbonded together to have a one-half inch overlap.

TABLE 2 Shear strength of bonded metal substrates. Substrate metal breakload (psi) aluminum 1700-2200 steel 2200 copper 1600These values are comparable to bonds formed using conventional epoxyresins. Thus, it is possible to form an electrochemically disbondablejoint without compromise to the mechanical strength of the bondedmaterials.

Lap shear tests were also performed to assess the effects of elevatedtemperature on the adhesive bond strength of bonded aluminum substratesformed using the formula of this example. The results are reported inTable 3.

TABLE 3 Shear strength of bonded aluminum substrates at varioustemperatures. temperature (° C.) break load (psi) 50 1800 60 1400 (yieldat 1000) 85 yield at 800

The bonded substrates were electrochemically cleaved at room temperatureby applying a 50V potential between the metal substrates. Disbondingoccurred at the anode. After 10 minutes, the substrates were easilysnapped apart by hand. The anodic interface was substantially free ofresidual resin.

Residual material of the disbondable compositions prepared from4,7,10-trioxi-1,13-tridecanediamine was removed from the cathodesubstrate using methanol.

EXAMPLE 3

This example demonstrates the effect of substitution of the amine curingagent on the strength and disbonding function of an epoxy composition.

An epoxy resin was prepared as described in Example 2, with substitutionof 4,7,10-trioxa-1,13-tridecanediamine with 15 parts tetraethylenepentamine (TEPA; CAS No. 112-57-2) to yield an electrocleavablecomposition having bond strengths of up to 2500 psi to aluminum at bothambient and elevated temperatures. The disbonding conditions and rateswere similar to those in Example 2. Disbonding occurred at the anode.

EXAMPLE 4

This example demonstrates the effect of substitution of theion-exchanged anion in PMS-g-PEO on the strength and disbonding functionof an epoxy.

An epoxy resin was prepared as described in Example 2, with substitutionof ammonium tetrafluoroborate for ammonium hexafluorophosphate to yielda resin that cured with increased hardness but with reduced roomtemperature conductivity. The observed increase in hardness is probablydue to increased ionic crosslinking.

Anodic disbonding of this resin can be achieved by applying a 50Vpotential across the bondline for 40 minutes at room temperature. Thelonger disbonding time of the formulation with ammoniumtetrafluoroborate is due to lower ionic conductivity of the material.

EXAMPLE 5

This example demonstrates the effect of plasticizer incorporation intothe composition on disbonding.

Ten parts octanol were added to the resin formulation of Example 3.Aluminum lap shear specimens bonded using the modified formulationexhibited shear strengths of 1600 psi and good mechanical properties.Application of a 50-volt potential at −20° C. resulted in disbonding inless than 15 minutes versus one hour for the unmodified version. At −40°C., disbonding occurred in less than 12 hours versus no disbonding forthe unmodified resin.

Thus, addition of plasticizer significantly improved the disbondingcapability of the formulation at lower temperatures, which hassignificant practical application where disbonding operations arerequired to take place outdoors or in other environmentally uncontrolledconditions. Presumably disbonding at room temperature will proceedsignificantly faster for the modified formulation.

EXAMPLE 6

This example demonstrates increased ionic conductivity due toheterogeneous curing of the matrix polymer.

Trioxadodecane-1,13-diamine (80 parts by weight) was added to 13Xzeolite powder (100 parts by weight) with stirring. The temperature ofthe mixture was allowed to increase as the amine adsorbed onto thesurface and interior of the porous powder. Amine/zeolite complex (160parts) were added to 100 parts DGEBA epoxy and 10 parts ammoniumhexafluorophosphate. Samples made by bonding together aluminumsubstrates using this formulation were cured at 80° C. for one hour andexhibited good adhesive bond strength. The material exhibited moderatelevels of ionic conductivity, about 1:10 that of the material of Example2. Application of a 50-volt current for two hours at room temperatureresults in weakening of the adhesive bond.

EXAMPLE 7

This example provides a composition disbondable at the cathodicinterface.

Poly(propylene glycol)bis(2-aminopropyl ether) (PPODA, CAS No.9046-10-1, M_(n) ca. 2000) was converted into the corresponding ammoniumsalt by an exchange reaction with ammonium hexafluorophosphate accordingto the reaction illustrated in Eq (1). To this end, PPODA (75 g) wasmixed with ammonium hexafluorophosphate (25 g) in a reaction vesselfitted with a mechanical stirrer and stirred for 48 hours at ambienttemperature and pressure.

A blend containing 100 parts of ion-exchanged PPODA and 100 parts thedisulfide epoxide of Example 1 was mixed with 8 parts dicyanodiamide.The mixture formed a strong bond to aluminum when cured at 100° C. for 4hours. The bond can be electrochemically disrupted by applying a 50Vpotential across the bond for 30 minutes at 40° C. Disbonding occurs atthe cathodic interface.

EXAMPLE 8

This example describes disbonding from a non-conductive substrate usinga conductive foil.

Aluminum foil (25 μm thick) was solvent degreased and etched withphosphoric acid and immersed in distilled water for one hour. Two sheetsof the dried foil were then bonded together using the resin of Example 1without crushed glass. The foil laminate was cured for one hour at 80°C. The foil laminate 69 is illustrated in FIG. 6A in whichelectrochemically disbondable composition 70 is sandwiched between foils72, 74.

The foil laminate 69 was then further bonded between two substrates. Thefoil laminate was cut to size appropriate for the substrates to bebonded. The external surfaces of the foil were coated with anamine-cured disulfide epoxy resin that is not electrochemicallydisbondable. The sandwich structure is shown in FIG. 6B, withconventional adhesive layers indicated as layer 76 and 78 (substratesnot shown). The adhesive-coated laminate was disposed between twosubstrates and pressure was applied using weights or clamps to keep theassembly together. The assembly was cured at room temperature for aperiod of 24 hours, resulting in a high strength, permanent bond.

The substrates are disbonded by disrupting the bond at the foilelectrochemically disbonding adhesive interface 80, which is indicatedin FIG. 6B. A 50V DC power source applied a potential difference acrossthe bonded structure for 10 minutes, after which the structure could besnapped apart by hand. The foil was peeled off of the still-attachedconventional epoxy layer. The substrate was cleaned of the residualadhesive by soaking in a solution of ammonia water, sodium3-mercaptopropyl sulfonate and methanol.

EXAMPLE 9

This example describes disbonding from a non-conductive substrate usinga conductive coating.

Non-conducting substrates were coated with a silver-filled epoxy.Connectors for external wiring were attached to the silver-filled epoxy.Following cure, a layer of electrochemically disbonding epoxy resin fromExample 1 was coated over the silver-filled epoxy. The coated substratesurfaces were mated and the resin was cured, forming an adhesive bond.This bond was electrochemically disbonded by attaching a 50V powersource either directly to the silver-filled epoxy layers or to theconnectors. Disbonding occurs in 20-40 minutes at room temperature,depending on the roughness of the silver epoxy.

EXAMPLE 10

This example describes disbonding of a coating.

The resin from Example 1 was coated directly onto a low carbon steelsurface as a primer layer. The coating can be applied from the bulkmaterial or by spraying a 50 wt % solution of the uncured resin in a 1:1mixture of nitromethane and methylene chloride. After drying, the primerlayer was overcoated with a thin layer of silver-filled epoxy and asuitable topcoat. The ionically conductive primer layer providedexceptionally good wet adhesion under highly corrosive conditions.Attachment of a 50V power source between the steel surface and thesilver-filled epoxy resulted in disruption of the adhesive bond betweenthe primer and the steel surface, allowing the coating to be easilyremoved by scraping. No corrosion was observed on the surface from whichthe coating was removed.

EXAMPLE 11

This example describes another method of disbonding a coating using anelectrolyte gel.

The resin from Example 1 was coated directly onto a low carbon steelsurface as a primer layer and allowed to cure. The cured coating wasthen electrically disbonded by the following procedure. A thickened gelcomprised of ammonium hexafluoride-exchanged PPODA was spread over thesurface of the primer-coating and physically contacted with a conductiveelement, such as a wire, mesh, foil or grid. Attachment of a 50V powersource to the steel surface (anode) and the conductive element (cathode)for a period of less than 20 minutes resulted in anodic disruption ofthe adhesive bond between the primer and the steel surface.

EXAMPLE 12

This example describes disbonding of a pigmented coating.

To 100 parts by weight of the material of Example 2, was mixed 65 partsby weight titanium dioxide (rutile) pigment to yield a white paint. Thispaint can be used to coat aluminum, steel or other metal surfaces. Thecoating was locally disbonded by contacting a conducting plate, coatedwith an ionically conducting gel, to the paint surface and attaching thepositive pole of a 50-volt power source to the coated substrate and thenegative pole of the power source to the conducting plate. After 10-15minutes, the paint was easily removed from the treated area by lightscrapping or peeling.

1. An electrochemically disbondable composition, comprising: a polymer;and an electrolyte, wherein the electrolyte provides sufficient ionicconductivity to said composition to enable a faradaic reaction at a bondformed between the composition and an electrically conductive surfaceand allow the composition to disbond from said surface.
 2. Thecomposition of claim 1, wherein said polymer has a variable crosslinkdensity to form regions of low crosslink density having a relativelyhigh ionic conductivity and regions of high crosslink density having arelatively high mechanical strength.
 3. The composition of claim 1,wherein said polymer includes coordination sites that are capable ofsolvating ions and that support the electrolyte functionality of saidcomposition.
 4. The composition of claim 3, wherein said coordinationsites are selected from the group consisting of alkoxy moieties,disulfide moieties, thioalkyl moieties, nitrile moieties, andpolyvinylidene fluoride moieties and derivatives thereof.
 5. Thecomposition of claim 1, wherein said electrolyte is localized in regionswithin said polymer to form a secondary phase with ionic conductivity.6. The composition of claim 1, wherein said electrochemicallydisbondable composition is a phase separated material having firstregions of substantially matrix functionality and second regions ofsubstantially electrolyte functionality.
 7. The composition of claim 6,wherein said electrolyte functionality comprises an ion solvatingmolecule that is selected from the group consisting of low molecularweight alkoxides, alcohols, alkyl carbonates, cyclic esters, nitriles,amides and ureas.
 8. The composition of claim 6, wherein said phaseseparated material comprises a block or graft copolymer containingnon-polar components and components of ionic conductivity.
 9. Thecomposition of claim 8, wherein said non-polar component of said blockcopolymer is selected to facilitate phase separation.
 10. Thecomposition of claim 1, further comprising a reservoir for containingcuring or crosslinking agent.
 11. The composition of claim 10, whereinthe reservoir is selected from the group consisting of zeolites, claysand polymer gels.
 12. The composition of claim 1 or 6, furthercomprising a salt capable of being solvated into said composition. 13.The composition of claim 12, wherein said salt is selected from thegroup consisting of alkali metal, alkaline earth and ammonium salts. 14.The composition of claim 12, wherein said salts include an anionselected from the group consisting of hexafluorophosphate,tetrafluoroborate, hexafluoroantimonate and perchlorate.
 15. Thecomposition of claim 12, wherein said salt is an ammonium salt and theammonium cation is immobilized in said composition.
 16. The compositionof claim 1 or 6, wherein said composition has an ionic conductivity inthe range of 10⁻¹¹ S/cm to 10⁻⁵ S/cm.
 17. The composition of claim 1 or6, wherein said composition has an ionic conductivity in the range of10⁻⁹ S/cm to 10⁻⁷ S/cm.
 18. The composition of claim 1 or 6, furthercomprising an additive selected from the group consisting of pigments,corrosion inhibitors, leveling agents, gloss promoters, rubbertougheners and fillers.
 19. The composition of claim 1 or 6, whereinsaid composition is an adhesive.
 20. The composition of claim 1 or 6,wherein said composition is a coating.
 21. The composition of claim 20,wherein said coating is resistant to delamination from a substrate towhich it is applied.
 22. A composition, comprising: a curable polymericmaterial comprising an epoxy; and an electrolyte located in said curablepolymeric material, said electrolyte being selected from the groupconsisting of ion solvating molecules, oligomers and polymers, andionomers, wherein said curable polymeric material, when cured, can formadhesive bonds with an electrically conductive surface, said adhesivebonds having a shear strength of greater than 200 psi, and saidcomposition has sufficient ionic conductivity to support a faradaicreaction at said electrically conductive surface, said faradaic reactionweakening said adhesive bonds.
 23. The composition of claim 22, whereinthe composition phase separates upon curing, said phase separatedmaterial having first regions of mechanical strength and second regionsof ionic conductivity.
 24. The composition of claim 22, wherein saidcurable polymeric material has an ionic conductivity in the range of10⁻⁹ to 10⁻⁷ S/cm.
 25. The composition of claim 1, wherein saidcomposition has a shear strength greater than 200 psi.
 26. Anelectrochemically disbondable composition bonded to a firstelectronically conducting surface and comprising an adhesiveincorporating an electrolyte imparting sufficient ionic conductivity tosaid composition to support a faradaic reaction at the bond between thecomposition and the electronically conducting surface when a voltage isapplied across the bond between the first surface and the composition,thereby inducing the composition to disbond from the first surface. 27.The composition of claim 26, wherein said adhesive is selected from thegroup consisting of epoxies, phenolics, acrylics, melamines, maleimides,polyurethanes, and combinations thereof.
 28. The composition of claim26, wherein said electrolyte is localized in regions within said polymerto form a secondary phase with ionic conductivity.
 29. The compositionof claim 28, wherein said electrolyte is selected from the groupconsisting of ion solvating molecules, oligomers, polymers, andionomers.
 30. The composition of claim 28, wherein said electrolytecomprises an ion solvating molecule that is selected from the groupconsisting of low molecular weight alkoxides, alcohols, alkylcarbonates, cyclic esters, nitriles, amides and ureas.
 31. Thecomposition of claim 26, further comprising a salt.
 32. The compositionof claim 31, wherein the salt is selected from the group consisting ofalkali metal, alkaline earth, and ammonium salts.
 33. The composition ofclaim 31, wherein the salt includes an anion selected from the groupconsisting of hexafluorophosphate, tetrafluoroborate,hexafluoroantimonate and perchlorate.
 34. The composition of claim 31,wherein the salt is an ammonium salt and the ammonium cation isimmobilized in said composition.
 35. The composition of claim 26,wherein said composition has an ionic conductivity in the range of 10⁻¹¹S/cm to 10⁻⁵ S/cm.
 36. The composition of claim 1, wherein a bond formedbetween the composition and an electrically conductive surface issubstantially weakened by application of an electrical voltage of 50volts after less than about 60 minutes.
 37. The composition of claim 26,wherein the bond is substantially weakened by application of anelectrical voltage of 50 volts after less than about 60 minutes.
 38. Thecomposition of claim 1, wherein the polymer constitutes at least 50% byweight of the composition.